1. Field of the Invention
The present invention relates to a channel equalizer in a digital TV receiver of a VSB (Vestigial Side Band) modulation system.
2. Description of the Related Art
In most of current digital transmission systems, and an ATSC (Advanced Television Systems Committee) 8VSB transmission system suggested as a digital TV (DTV) transmission system for the USA, when a broadcasting signal is transmitted on a channel through air or a line, the digital TV receiver receives the broadcasting signal together with signals reflected at different reflectors. Since the reflected components distort an original signal, it is impossible to obtain the original signal only from the received signal. The components that distort the original signal are ghost, or fading, or the like.
The signal distorted thus causes a bit detection error at the digital TV receiver, such that restoration of a whole picture is impossible, or a totally different picture is displayed.
In order to overcome this, the digital TV receiver is provided with the equalizer to compensate for the component (i.e., the ghost, or the fading) that distorts the transmitted signal between a transmitter terminal and a receiver terminal.
In the equalizers, there are time-domain equalizer, and frequency-domain equalizers, all of which serve for removing the component that distorts the original signal.
The frequency-domain equalizer estimates an impulse response of a channel from a time domain signal, and converts the channel impulse response into a frequency domain signal. Then, the frequency-domain equalizer controls parameters of the frequency-domain equalizer so that the frequency domain signal distorted on the channel becomes an ideal frequency domain signal, for correcting the distortion. That is, after a received time domain signal is converted into a frequency domain signal, the frequency domain equalizer compensate for the faded components. Then, the compensated frequency domain signal is converted into a time domain signal, again.
In this instance, when a signal having a fading passes through the frequency-domain equalizer, though the fading is compensated, an amplification of a noise is taken place.
FIG. 1 illustrates a block diagram of a channel equalizer in a related art digital TV receiver with a frequency-domain equalizer and a noise removing part, wherein a demodulating part 101 tunes to a desired channel from RF (Radio Frequency) signals received through an antenna, converts a RF signal on the tuned channel into an IF (Intermediate Frequency) signal, demodulates the IF signal in reverse of a VSB modulating system, and provides to the frequency-domain equalizing part 102. Then, the frequency domain equalizing part 102 estimates the impulse response of the channel from the time domain signal received thus, converts the channel impulse response estimated thus into a frequency domain signal, and compensates for fading components thereof by controlling parameters, and provides to a noise removing part 103. The noise removing part 103 removes noise amplified at the time of equalizing from an output of the frequency domain equalizer 102.
The frequency-domain equalizer 102 requires a signal the same with a field sync as shown in FIG. 2 for estimating the channel impulse response.
FIG. 2 illustrates a data frame architecture at a digital TV receiver of a VSB system, wherein one frame has two fields, and one field has 313 data segments. One data segment has 832 symbols. In the data segment, first four symbols are segments synchronizing part, and in the field, a first data segment is a field synchronizing part.
That is, in the VSB data frame structure in FIG. 2, a field synchronizing signal appears at every 24.2 ms. Therefore, the parameter renewal at the frequency-domain equalizer is made at every 24.2 ms.
Accordingly, in a channel environment in which the fading is faster than 24.2 ms, the frequency-domain equalizer in FIG. 1 can not compensate for the fading, properly. That is, since there are many cases the fading is faster than 24.2 ms in an actual environment, the equalizer in FIG. 1 can not provide a proper performance.